1. Field of the Invention
The present invention relates to an optical fiber fusion splicer that axially aligns optical fibers by clamping with a V-shaped groove, and more particularly, to an optical fiber fusion splicer that enables reliable end alignment of the optical fibers without allowing their axial centers to shift from the proper position even if the outer diameters of the optical fibers and jackets change.
2. Description of the Related Art
FIG. 3 schematically illustrates an optical fiber fusion splicer of the prior art in which the end aligned portions of optical fiber cores are observed from the side by clamping the jackets of optical fiber cores in a V-shaped groove. In FIG. 3, jackets 32 of left and right optical fiber cores 30 are respectively clamped between the a V-shaped groove of a V-shaped groove base 34 and a clamp 36. Axial alignment of the optical fiber cores 30 is performed using an observation means having bi-directional image observation optical axes A that combine a microscope 40 and a TV camera 42 by observing the end aligned portions 44 of the cores on a monitor 46, processing observation information from the two directions with a processor 48, transmitting the output signal to a movement mechanism (not shown) of the V-shaped groove bases 34, moving the V-shaped groove bases 34 to axially align with the two-dimensional X and Y directions at a right angle to the axis of the optical fiber cores 30, advancing in the direction of the cores (Z direction) and then generating an electrical discharge to fuse and splice the cores. In this optical fiber fusion splicer, when the optical fibers are placed in the V-shaped grooves of the V-shaped groove base 34, the height of the V-shaped groove bases 34 is adjusted so that the axis in the direction of the cores of the optical fibers is located in the vicinity of the proper position between electrodes 50 of electrical discharge for optimum fusing of the optical fibers. Moreover, in the case of observing images from two directions, the optical fibers are placed so that the intersection of the image observation optical axes A in two directions is located at the above proper position between the electrodes 50. FIGS. 4A and 4B show the relationship between the electrodes 50 and the image observation optical axes A when the jacket 32 is placed in the V-shaped groove 34a of the V-shaped groove base 34. FIG. 4A indicates the case of a sheath diameter of 250 xcexcm, while FIG. 4B indicates the case of a sheath diameter of 400 xcexcm. In FIG. 4A, a center point O, which is the intersection of image observation optical axes A, is set at the proper electrical discharge position between two stationary electrodes 50, and if the optical fiber core 30 having a sheath diameter of 250 xcexcm is placed on the V-shaped groove base 34 exclusively for use with a sheath diameter of 250 xcexcm and having the V-shaped groove 34a formed therein so that the center of the core 30 coincides with the proper electrical discharge position and the center point O of the image observation optical axes, the image of the end aligned portion 44 can be captured without shifting from the proper position between the electrodes 50 or from the image observation optical axes A in two directions.
When an optical fiber core 30xe2x80x2 having a sheath diameter of 400 xcexcm is placed in the V-shaped groove base 34 in this state, as indicated with the broken lines in FIG. 4A, the center position of the optical fiber core 30xe2x80x2 moves upward by a height corresponding to the difference in sheath thickness of 75 xcexcm from the center position 0 of the optical fiber core 30 having a sheath thickness of 250 xcexcm. This height is equal to 75xc3x97{square root over (2)}=106 xcexcm in the case the angle formed between the slanted surface of the V-shaped groove 34a in contact with the optical fiber core 30 of the V-shaped groove base 34 and the upper and lower directions of the V-shaped groove 34a is 45 degrees.
Therefore, although it is necessary to move the V-shaped groove base 34 downward by the amount of this height in order to return this center position to the proper electrical discharge position, in the case of the X and Y direction movement mechanism of the V-shaped groove base 34 of the fusion splicer of the prior art, such movement in the vertical direction was difficult for the reasons described below.
FIGS. 5A and 5B are drawings of the left and right V-shaped groove bases 34 of a fusion splicer of the prior art as viewed from direction B in FIG. 3. As shown in FIGS. 5A and 5B, a V-shaped groove movement mechanism is placed so as to be able to move in two directions of movement of X and Y that are respectively perpendicular to each of the two directions of the image observation optical axes A so that observation images are not shifted out of focus due to the movement of the V-shaped groove 34a. 
On the other hand, the two directions of the image observation optical axes A are set so as to be mutually perpendicular to facilitate coordinate conversion during image processing, and the two directions of the image observation optical axes A normally coincide with axial directions X and Y at a right angle which form a 45 degree angle with the vertical direction of the V-shaped groove 34a as shown in FIG. 3. Moreover, the movement mechanism of the left and right V-shaped grooves 34a in which left and right optical fiber cores 30 are respectively placed is normally composed so as to only allow movement in one mutually different direction of movement of the above two directions of movement in order to simplify the drive mechanism.
Thus, since the left and right V-shaped grooves 34a are only able to move in one direction that forms a right angle to the left and right in a direction that forms a 45 degree angle with the vertical direction of the V-shaped grooves 34a, it was difficult to move the left and right optical fiber cores equally in the vertical direction. In addition, in a device equipped only with this type of centering mechanism, it was not possible to correct shifts in the proper electrical discharge position or observation optical axes of 10 xcexcm or more.
In addition, even if the V-shaped groove movement mechanism is not that which only allows movement in one direction for each side of the left and right V-shaped grooves 34a, since the purpose of the movement mechanism is to adjust slight axial shifts of the left and right optical fibers, the distance range over which movement is possible is limited by the movement resolution (on the order of 0.1 xcexcm or less). Since such a mechanism makes movement of several tens of xcexcm or more difficult, movement of several tens of xcexcm or more due to differences in sheath thickness in the vertical direction of the V-shaped groove surface was difficult.
Thus, during optical fiber core 30xe2x80x2 having a sheath diameter of 400 xcexcm, it was necessary to either replace the V-shaped groove bases 34 with V-shaped groove bases 34xe2x80x2 in which deeper V-shaped grooves 34axe2x80x2 are formed, or move the electrode rods and image observation system in the vertical direction.
However, a material such as ceramics that allows high-precision machining was used for the V-shaped groove bases 34, 34xe2x80x2 based on its role of maintaining parallelism and so forth. Thus, the providing of multiple V-shaped groove bases to match variations in sheath diameter was expensive. Moreover, the work involved in replacing the V-shaped groove base 34 required a high level of accuracy, and required an extremely delicate procedure. In addition, although another method for aligning the center of an optical fiber core at the proper electrical discharge position between two electrodes 50 without replacing the V-shaped groove base 34 is known in the prior art in which the electrodes and image observation optical axes are simultaneously moved up and down until they reach the center of the optical fiber core, this makes the overall device complex. Moreover, such a method also has the disadvantages of not being able to be used for splicing fibers having different coating diameters, adjustment being complicated and costs being high.
Moreover, since a material that allows high-precision machining is required to be used for the V-shaped groove base 34 as previously mentioned, if ceramics, for example, is used, the coefficient of friction is comparatively large at 0.6 to 0.8. Consequently, in combination with the sinking action of the sheath due to elastic deformation of the jacket 32, a phenomenon occurs in which the optical fiber core 30 is lifted up on the surface of the V-shaped groove 34a as shown in FIG. 6 during the rotation alignment procedure for constant polarization optical fibers. As a result, the optical fiber core 30 shifts from the image observation optical axis A causing images to be out of focus and resulting in error in analysis of the plane of polarization.
In consideration of the various problems of optical fiber fusion splicers that perform end alignment by the above observation means, the object of the present invention is to provide an optical fiber fusion splicer that enables the axial center of an optical fiber core to be positioned at a suitable electrical discharge position and in the center of an image observation optical axis at all times regardless of the magnitude of the optical fiber diameter, and enables analysis of the plane of polarization to be performed accurately even if a phenomenon involving lifting up of the optical fiber core occurs during rotation alignment of a constant polarization optical fiber.
In order to achieve the object, an optical fiber fusion splicer of the present invention equipped with: a V-shaped groove base that respectively fixes and clamps left and right optical fibers in a V-shaped groove and a clamp for fixing optical fibers in the V-shaped groove, an observation means for observing the left and right optical fibers from the side, a V-shaped groove movement mechanism that aligns the end surfaces of optical fibers by performing axial alignment of the left and right optical fibers based on observation information from the observation means, and electrodes that generate an electrical discharge at the aligned portions to fuse and join them; wherein, a V-shaped groove base vertical movement means is provided that moves the V-shaped groove base up and down so that the centers of the axes of the optical fibers are positioned at the proper location for electrical discharge corresponding to the magnitude of the optical fiber diameter.
According to this optical fiber fusion splicer, although the position of the axis center of the optical fiber core changes relative to the V-shaped groove depending on the magnitude of sheath diameter, since the V-shaped groove base that holds the core is moved up and down according to that sheath diameter, the axis center of the core can be positioned at the proper position for electrical discharge. Thus, end alignment work can be performed reliably without the axis center shifting from the proper position for electrical discharge using only a simple mechanism in the form of the V-shaped groove base vertical movement means.
In the optical fiber fusion splicer, it is preferable that the observation means has observation axes in two directions which mutually form a right angle, the intersection of the observation axes in two directions is located at the proper location for the electrical discharge, and the V-shaped groove movement mechanism has a means for moving at least one of either of the left and right optical fibers in a direction that forms a right angle with the observation axes in two directions.
According to this optical fiber fusion splicer, since the V-shaped groove base that holds the core is moved up and down corresponding to sheath diameter, the axis center of the core can be aligned with the image observation optical axis. Thus, end alignment can be performed reliably without the axis center shifting from the image observation optical axis using only a simple mechanism in the form of the vertical movement mechanism of the V-shaped groove base.
Furthermore, in the optical fiber fusion splicer, a rotation mechanism for rotating the axis of the optical fiber, and a means which can separately move up and down the V-shaped groove base and the clamp relative to the surface of the V-shaped groove corresponding to information from a lateral observation means during optical fiber rotation, can be provided.
According to this optical fiber fusion splicer, when the phenomenon of fiber lift-up is captured by the observation means during rotation alignment of a constant polarization optical fiber core, since the optical fiber core is re-clamped after temporarily moving the clamp upward and the V-shaped groove base downward, the lift-up phenomenon can be eliminated thereby enabling analysis of the plane of polarization to be performed accurately.